328 II. C. Bradley — Color Reaction for Copper. 



10 per cent strength is convenient — and to remove the copper 

 by H 2 S. In such solutions of tissue ash as were used in our 

 experiments, copper was first removed and the filtrate contain- 

 ing iron, calcium, phosphoric acid, etc., concentrated to small 

 bulk. A drop of this solution placed on a microscope slide 

 and digested with a drop of the freshly prepared nitroprusside 

 solution, deposited on cooling the rectangular plates and prisms 

 of the zinc salt when that metal was present in such minute 

 amounts that the ordinary methods of separation and identifi- 

 cation failed to show it definitely, or required the ashing of 

 large amounts of the original material. For example, by this 

 method zinc was detected readily in the blood of certain mol- 

 luscs in a few minutes, while by the ordinary methods of 

 separation and analysis — the basic acetate method, or better, 

 the precipitation of the metal as sulphide from a formic acid 

 solution — many hours are required to ash sufficient material 

 and carry through the steps of the analysis. 



